It is known in the prior art to use vehicles as probes for measuring traffic conditions in real-time. Individual vehicles provide “floating car data,” such as, for example, the vehicle's time, speed, position, and heading, which can be used to estimate travel time and traffic speed, and which can in turn be used as an online indicator of road network status, as a basis for detecting incidents, or as input for a dynamic route guidance system.
With reference to FIG. 1 (PRIOR ART), an exemplary prior art probe vehicle system 10a typically includes a plurality of probe vehicles 12a; technology 14a for determining each probe vehicle location, such as, for example, a system using orbiting satellites, such as the Global Positioning System (GPS), a system using cellular telephones, or a system using radio-frequency identification (RFID); and a wireless communication system 16a for allowing communication between the vehicles 12a and a traffic information center (TIC) 18a. Typically, the center 18a receives and processes the data generated by the probe vehicles 12a, and then transmits the data to a plurality of receiving vehicles, which may further include non-probe vehicles 20a. Constant communication between the probe vehicles 12a and the center 18a requires the storage of a voluminous amount of data.
One type of traffic control system categorizes geographic thoroughfare sections as links and utilizes generally constant probe vehicle data within a set of link coordinates to reach a general link condition. Other receiving vehicles located upon the link receive the pre-determined general condition, which is constantly being updated by the probe vehicles upon the link. Using traffic simulation methods, different studies have provided widely varying estimates of the number of probe vehicles needed to accurately determine a general link condition. These studies indicate that, on a freeway, for example, 2% to 7% of the vehicles present must be probe vehicles providing data in order to determine real-time traffic conditions with a sufficiently high level of confidence. Even in this configuration, however, an exceedingly large number of probe vehicles are typically required to communicate with the center to transmit and store large amounts of data; and here, again, exceedingly substantial data processing capacity remains necessary at the center to process a large volume of incoming data in real-time.
In another prior art configuration, the transmission of traffic data between the center and vehicles is reduced by limiting transmissions to instances where one of a pre-determined set of conditions is achieved. In other words, the probe vehicle communicates traffic data to the center only when sensors indicate that at least one of a plurality of triggering conditions exist. However, like the other traffic control systems, this configuration requires that large sets of data, i.e. pre-determined triggering condition data, be stored on-board each probe vehicle.